Internally Shorted 30Amp Power Pedestal Plug

[SuperD]

This happened to us last week, poor connection on 120v for water heater which caused arcing and burning. Luckily we were in the coach and awake, smelled the burning and shut off the water heater before a fire started.

[Chance]

Originally Posted by JamieGeek

Right but your use case is a little different: Since you're renting there you kind of are looking around because it isn't your camper so you are doing extra checks.

If it was your camper you may give it a once over at the beginning of the season and then not think twice about anything. Why would you/us? It worked before and no one else has touched it.

May be unusual, but I check my own equipment a lot more than rentals. I have the attitude that the cost premium I pay should include the rental company looking after their property (don't rent from private individuals), and that I shouldn't have to. I mostly check items that could affect my safety, like tires. We also camp/travel year round so it's an ongoing process.

The plug problem I had was with last unit I rented -- haven't been renting as much lately because my parents can't travel with us any longer. When it's just the two of us we prefer the smaller van so no need to rent a MH or a trailer.

I was lucky to have been carrying my own 30-Amp extension from van so was able to rig a temporary fix to get us home. Since that incident is when I started checking plugs a few times a year. I don't obsess about it though.

[Thehobe1]

The power connections are probably at fault here. As connector pins wear or even under heavy loads (air conditioner starting currents), the pin connections are not very good when left connected for long periods of time. Normally, when plugging in plugs, there is a wiping action that helps to give a "cleaning" to the contact surfaces. When high current loads switch on and off, (air conditioner) motor back EMFs can result in much high switching currents that can cause arcing across the connection surfaces resulting in surface oxidation. As this oxidation increases, resistance builds up in the physical connection resulting in heat being generated by IxR (current times voltage) loss in the pin contact area. Unfortunately heat results in more oxidation, more resistance and even more heat. When the air conditioner is on and drawing let's say 15 Amperes, the air conditioner continues to operate even when the AC power drops to 90VAC. In this case, there is (15A)(120VAC-90VAC) = 450 Watts! This is more than enough power to melt the socket and it's surroundings. Note that the breaker will NOT trip because the current is well below 30A. Surge protectors trip typically at 170VAC and also do not see any issue with the incoming AC voltage. Surge protectors are fairly small electronic devices that breakdown (provide a very low resistance) when voltages exceed their breakdown rating which results in overcurrent that trips a breaker. There is NO excessive voltage here, just a lot of power being dissipated in the plug/socket connection.
The connections in these RV parks are typically very worn already and can also cause extreme heat in the RV service box when providing heavy air conditioner or oven type loads.
By the way, when you first turn on an incandescent 100 Watt light bulb, the inrush current is typically 10 times the nominal current for just a few 10s of milliseconds until the filament warms up! Air conditioners are kind of the same idea, initially they draw much more (stall) current until the motor speed up from it's stopped condition. Circuit breakers and fuses are built to pass these higher current for a short amount of time but contacts can degrade under these conditions.
I would suggest to all RV'ers that they feel their plug connections after 10-20 minutes of running the high current loads including air conditioners, ovens, washing machines and electric dryers to make sure they can feel the warmth of the plug under normal conditions so they would know what normal feels like.

[mountainsam]

Originally Posted by SuperD

This happened to us last week, poor connection on 120v for water heater which caused arcing and burning. Luckily we were in the coach and awake, smelled the burning and shut off the water heater before a fire started.

SuperD, This happened in your 2017 Windsport?

[Thehobe1]

Originally Posted by SuperD

This happened to us last week, poor connection on 120v for water heater which caused arcing and burning. Luckily we were in the coach and awake, smelled the burning and shut off the water heater before a fire started.

Attachment 7903

Attachment 7904

It looks to me like the strands from one of the connecting wires was not originally held within the "spring" that is meant to apply pressure between the wires being connected. WOW, electrician 101! Is this the case; I can't quite see it in the picture.

[Kev]

Glad you are ok. I keep thinking what if this happen to us when we are away from the coach with pets inside.

[Porkchop]

Thehobe1=This thread has been populated by good meaning people who are very weak in electrical theory and application, but you just topped the cake! Don't hand out advice that could hurt people even if your intentions are good.
Please explain your a/c with low voltage pulling more watts but less amps to this retired, 40 years of practical electrical engineering and installation person. Same with the light bulb. And your view of a typical RV "surge suppressor". That one really excites me.
"Fairly small with a circuit breaker"

Bill

[16ACE27]

Originally Posted by Thehobe1

The power connections are probably at fault here. As connector pins wear or even under heavy loads (air conditioner starting currents), the pin connections are not very good when left connected for long periods of time. Normally, when plugging in plugs, there is a wiping action that helps to give a "cleaning" to the contact surfaces. When high current loads switch on and off, (air conditioner) motor back EMFs can result in much high switching currents that can cause arcing across the connection surfaces resulting in surface oxidation. As this oxidation increases, resistance builds up in the physical connection resulting in heat being generated by
CUT
" IxR (current times voltage) loss in the pin contact area" IxR is NOT current times voltage, it is voltage drop. You are trying to describe I(squared)R losses which is power lost due to heat generated by resistance.
CUT
Unfortunately heat results in more oxidation, more resistance and even more heat. When the air conditioner is on and drawing let's say 15 Amperes, the air conditioner continues to operate even when the AC power drops to 90VAC.
CUT
Power is not measured in "VAC"
CUT
In this case, there is (15A)(120VAC-90VAC) = 450 Watts! This is more than enough power to melt the socket and it's surroundings. Note that the breaker will NOT trip because the current is well below 30A. Surge protectors trip typically at 170VAC and also do not see any issue with the incoming AC voltage. Surge protectors are fairly small electronic devices that breakdown (provide a very low resistance) when voltages exceed their breakdown rating which results in overcurrent that trips a breaker. There is NO excessive voltage here, just a lot of power being dissipated in the plug/socket connection.
The connections in these RV parks are typically very worn already and can also cause extreme heat in the RV service box when providing heavy air conditioner or oven type loads.
By the way, when you first turn on an incandescent 100 Watt light bulb, the inrush current is typically 10 times the nominal current for just a few 10s of milliseconds until the filament warms up! Air conditioners are kind of the same idea, initially they draw much more (stall) current until the motor speed up from it's stopped condition. Circuit breakers and fuses are built to pass these higher current for a short amount of time but contacts can degrade under these conditions.
I would suggest to all RV'ers that they feel their plug connections after 10-20 minutes of running the high current loads including air conditioners, ovens, washing machines and electric dryers to make sure they can feel the warmth of the plug under normal conditions so they would know what normal feels like.

[Thehobe1]

Tfryman:
You are correct with some of my incorrect verbiage at times. It is I squared x R to get power but I was just trying to emphasize that the oxidized contact resistance is where the heat is being generated.
Also, when I talk about AC power, I am referring to the power loss across the oxidized/corroded resistance giving rise to the resulting heat. I know it is related to the RMS AC x the RMS I, not taking into account the exact phase relationship. I do not want to get too technical and am sorry if I hurt your feelings.
Also, most "surge suppressors" are actually just tranzorbs that look like little ceramic capacitors that break down due to the instantaneous peak voltage applied across the tranzorb. Fast and short rise time voltage transients or spikes are absorbed by these units but will fail if to much or too long a transient persists resulting in too much internal heat, rendering the tranzorb into a very low resistance that trips some safety device such as a fuse or a circuit breaker. I know you probably are familiar with these devices.

I just get tired of everybody thinking that the melted connector is a result of a "short circuit" when if it was truly a short circuit, a circuit breaker would trip. If there was no circuit breaker, and there is a true short circuit, sparks would really fly.

[Porkchop]

WOW, a whole bunch of new words and theory. Are you reading all this junk out of a 4th grade science book? QUIT IT!!!NOW!!!

Bill

[gnach]

Allow me to jump into the flame war. Porkchop- thanks for the pedantic critique of Thehobe1's post without contributing anything to the topic that might reflect your vast experience. Sheez.

My takeaway here is that the sockets/receptacles we connect our electrical power will wear with usage and need inspection and possibly periodic replacement. The "spring" grip of the socket (call them "clips" maybe?) soften with the heat generated by the current flow. We all know that wall outlet at home that the vacuum gets plugged into. As the grip relaxes, a small gap begins to grow but the demand of the load continues and the electricity will arc across the gap accelerating the deterioration with more heat. Ed's MH is well used and has been connected/disconnected often. Add in the external connector supplied isn't exactly industrial grade AND the possibility that the wires weren't tight to begin with. Electrical connections should be checked and re-tightened periodically. I intend to check all the connections in mine.

I like Thehobe1's suggestion to take a hold of the plug connectors of running (operating) appliances to be familiar with normal warmth but to feel the main cord connector at the MH too. They should never feel hot.

[Bob Denman]

Let's all take a dep breath, and have a dish of ice cream...

[Porkchop]

Some statements are so far afoul and incorrect they must be immediately shot. No chance of rehab. No correcting something so off base. Even if it is populated with big, incorrect terminology.

Bill

[tigwelder]

so who is winning the Navy or pork chop?

[SuperD]

You get a bad connection, it gets hot and melts, and this is bad. Got it!

[SuperD]

Originally Posted by mountainsam

SuperD, This happened in your 2017 Windsport?

Yes. About 8pm we were watching tv when the smell began, took a few minutes to track down the source of the smell. When I opened the cabinet doors under the sink the smell was very intense and I figured it had to be the water heater. I immediately shut off the power, it was on AC at the time, opened the door, and turned on the vent fans to get rid of the smell. There was no smoke but a close inspection with a flashlight showed the black plastic box on the back of the water heater was partially melted so I knew this was the source. It was still early in the evening so I went ahead and made the repair. Also found out the breakers were not labeled correctly, got my eyeballs lit up while making the repair. My fault for not checking power with a meter, I know better but was in a hurry which always guarantees a surprise!!!

Again, glad we were awake and in the coach when the event occurred, could have been disastrous otherwise.

[SuperD]

Originally Posted by Thehobe1

It looks to me like the strands from one of the connecting wires was not originally held within the "spring" that is meant to apply pressure between the wires being connected. WOW, electrician 101! Is this the case; I can't quite see it in the picture.

The connection is stranded to solid core. A close inspection, not visible in the picture, showed the stranded wire to have only had the insulation stripped off by about 1/8” and the solid core about 1”, not conducive to make a good connection in the wire nut. The only thing holding the connection together was the foot long piece of electric tape wrapped around the wires and wire nut! Suprized the connection didn’t fail sooner.

[gnach]

As a follow up to my post about loose connections, user mcr1010 had the exact same problem but found it before it got too bad, Thor Forums - View Single Post - Another bad elec. connection
Exactly as I speculated, the inside connection was never tightened during construction! WE are the final QC inspectors and sometimes it takes a near catastrophe to get our attention. Shame on Thor!